Semiconductor memory devices, including Dynamic Random Access Memories (DRAMs), Static Random Access Memories (SRAMs), Electrically Erasable Programmable Read Only Memories (EEPROMs), and the like typically include an array of memory cells. The array of memory cells may be arranged in rows and columns. Such cells store information in one of two states, namely a logic high state (a logic "1" state) or a logic low state (a logic "0" state). To access this binary form of information, a unique address is employed. The address is based on column and row locations. The address is decoded by address decode circuitry for identifying the particular row and column of the memory array. In manufacturing such memories, it is sometimes found that a memory cell does not function properly. Accordingly, an address to such a defective cell is identified and rerouted to a redundant memory cell. For this rerouting, the defective memory array address is programmed in a fuse or antifuse bank. The latter being especially applicable to repair a defective die after encapsulation. In this manner, if an address is received to a memory, and it matches a programmed defective address stored in a bank, the bank associated with a redundant location in the array reroutes the access to the redundant location. The redundant location is usually a redundant row or column.
Antifuses for redundant memory applications are generally constructed in the same manner as memory cell capacitors. The antifuse acts as a relative open circuit until programmed. Once programmed, the antifuse acts as a relative short circuit. By relative open circuit and relative short circuit, it should be understood that measurable resistance values exist in both states. In order to program an antifuse, a voltage, often referred to as a programming or super voltage, is applied to the antifuse to cause breakdown of the dielectric material interposed between two capacitive plates. The applied voltage will depend on the voltage required to break down the dielectric for purposes of making it sufficiently conductive; in other words, lowering the dielectrics' resistance to an acceptable limit. Programmed antifuses and unprogrammed antifuses in a bank therefore may be used to represent a binary address.
Conventional memory modules typically have one or more memories attached to a circuit board. Examples of such modules include: Single In-Line Memory Modules (SIMM), Dual In-Line Memory Modules (DIMM), and Multi-Chip Modules (MCM), the latter of which is typically assembled with multiple dies prior to packaging.
In the past, after a die was packaged, it was mounted to a circuit board to form a module, and installed in a computer, to effect any rerouting of defective cells to redundant cells necessitated removal of the defective memory module. Memory is typically installed in a personal computer or work station. Consequently, if a single bit in a memory fails (single bit errors are a typical type of latent defect or field failure), the defective memory or memory module in a computer heretofore was removed from the computer and either disposed of or returned to the manufacturer. Therefore, it would be desirable to selectively repair bit errors in a memory array, and particularly a memory array of a memory module, located in a personal computer without having to uninstall memory.